As is well known, polymers containing both aromatic and ethylenic unsaturation can be prepared by copolymerizing one or more polyolefins, particularly a diolefin, with one or more alkenyl aromatic hydrocarbon monomers. Other diolefins such as 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene and the like, and other vinyl aromatic hydrocarbons such as o-methylstyrene, p-methylstyrene, p-tertbutylstyrene, 1,3-dimethylstyrene, alphamethyl-styrene, vinylnapthalene, vinylanthracene and the like may be used. The copolymers may, of course, be random, tapered, block or a combination of these. Radial and star polymers are also well known.
Polymers containing ethylenic unsaturation or both aromatic and ethylenic unsaturation may be prepared using free-radical, cationic and anionic initiators or polymerization catalysts. Such polymers may be prepared using bulk, solution or emulsion techniques. In any case, the polymer containing at least ethylenic unsaturation will, generally, be recovered as a solid such as a crumb, a powder, a pellet or the like. Polymers containing ethylenic unsaturation and polymers containing both aromatic and ethylenic unsaturation are, of course, available commercially from several suppliers.
Polymers of conjugated diolefins, polymers of vinyl aromatic hydrocarbons and copolymers of one or more conjugated diolefins and one or more alkenyl aromatic hydrocarbon monomers such as ABA block copolymers, including radial and star versions, are frequently prepared in solution using anionic polymerization techniques. In general, when solution anionic techniques are used, these polymers are prepared by contacting the monomers to be polymerized simultaneously or sequentially with an organoalkali metal compound in a suitable solvent at a temperature within the range from about -150.degree. C. to about 300.degree. C., preferably at a temperature within the range from about 0.degree. C. to about 100.degree. C. Particularly effective anionic polymerization initiators are organolithium compounds having the general formula: EQU RLi.sub.n
Wherein: R is an aliphatic, cycloaliphatic, aromatic or alkyl-substituted aromatic hydrocarbon radical having from 1 to about 20 carbon atoms; and n is an integer of 1 to 4.
Such polymers are then often coupled to produce longer linear polymers or radial or star polymers by reacting the living polymer chains or arms with a polyfunctional coupling agent. This process is described in detail in U.S. Pat. No. 4,096,203 which is herein incorporated by reference. A well-known coupling agent for use in making star polymers is a polyalkenyl aromatic coupling agent, specifically divinyl benzene. The present invention provides an alternative coupling agent for use in producing such polymers.